1. Field of the Invention
The invention in general relates to preamplifiers for oscilloscopes or other electronic instrumentation devices, and more particularly to such a preamplifier that includes a cross point multiplexer.
2. Description of the Related Art
In this disclosure "instrumentation" means the area of the electronic art in which analog signals are transmitted with high signal integrity over a wide band-width. An oscilloscope is an example of such an instrumentation device. Oscilloscopes and other instrumentation devices often include a preamplifier, usually referred to as a preamp. Since oscilloscopes and other instrumentation devices must be capable of distinguishing small nuances of signals of a wide spectrum of frequencies, such preamps must also be capable of amplification with high signal integrity over a wide band width.
State-of-the-art oscilloscopes employ analog to digital signal acquisition systems, thus new generation oscilloscopes include analog to digital converters. The requirement of high signal integrity, and the inherent limitations of analog to digital converter technology, limits the sample rate that can be achieved in such analog to digital converters. The limitation on sample rate necessarily implies a limitation on band width.
To overcome the band-width limitation, oscilloscope preamps have been developed that include multiple outputs each of which can be connected to a analog to digital (A/D) converter. The outputs of the A/D converters are then interleaved to produce a high sample rate.
Present-day electronic circuits are becoming more and more complex, with ever-increasing numbers of circuit nodes, such as pins, to be tested. Thus, another direction that the art of oscilloscope preamp has taken is to provide several channels in the preamp, each channel carrying a different signal.
Current oscilloscope preamps make trade-offs between available channel count and sample rate. However, the needs of a user may change, or vary from project to project. Thus, an oscilloscope preamp purchased with an eye toward high channel count may come up short if a project calls for high sample rate, and vice-versa.
Oscilloscope amplifiers also generally include variable attenuators in the front end. These typically are mechanical switches that are manually set on the front of the preamp. Since each channel must have such an attenuator, this requirement of an attenuator puts significant constraints on how many channels can be included in a reasonably sized preamp, and also adds significantly to the cost of a many-channel preamp.